Topics of current studies include: 1) characterization of unusual strains of Thermoascus crustaceus isolated from the monocytes of AIDS patients, 2)\isolation of an isogenic sets of C. albicans including extracellular proteinase positive wild type, negative mutant and positive revertants to compare their virulence for mice, and 3) determination of geographic distribution of the two varieties of C. neoformans. Three isolates of Thermoascus crustaceus were isolated from monocyte cultures of patients suffering from AIDS. The three isolates were atypical in that the ascospores had smooth wall while those of the typical T. crustaceus were echinulate. The atypical T. crustaceus has not been reported from clinical specimens. The mycelial extracts of these AIDS isolates produced immuno-suppressive material as determined by lymphocyte bioassays. When the spores of T. crustaceus were injected into mice intraperitoneally, the spores did not germinate but survived in mouse tissue for three to six weeks. Extracellular proteinase has been implicated as a virulence factor in Candida albicans. We were successful in isolating isogenic sets of strains including proteinase positive wild type, negative mutant and the positive revertant originating from one isolate. These isolates will be tested for their virulence for mice. The epidemiological differences between the two varieties of Cryptoccoccus neoformans were studied using 725 clinical isolates obtained from various parts of the world. It showed that the C. neoformans var. gattii (serotype B.C) is prevalent only in tropical and subtropical regions of the world while C. neoformans var. neoformans is prevalent throughout the world. C. neoformans var. gatti is not found in Europe and Japan. In the United States, C. neoformans var. gatti is prevalent only in Southern California and is infrequently found from the remaining part of the U.S.